1. Technical Field
This invention relates generally to devices for use in the medical arts. More particularly, the invention relates to a tip for use with a device for separating an implanted elongated structure, such as an implanted electrical pacemaker or defibrillator lead, from encapsulating biological tissue.
2. Background Information
A variety of medical treatments and surgical methods entail implanting an elongated structure in the body of a human or veterinary patient. Examples of such elongated structures include catheters, sheaths and cardiac electrical leads (such as pacemaker leads and defibrillator leads), as well as a variety of other devices. Over time, it can become necessary or desirable to remove the implanted elongated structure from the body of the patient. However, if the elongated structure has been implanted for an extended period of time, encapsulating biological tissue can grow around the elongated structure, making it difficult to remove the structure from the encapsulating tissue.
A heart pacemaker is typically implanted in a subcutaneous tissue pocket in the chest wall of a patient. A pacemaker lead extends from the pacemaker through a vein into a chamber of the patient's heart. The pacemaker lead commonly includes a conductor, such as an electrical wire coil, for conducting electrical signals (such as stimulating and/or sensing signals) between the pacemaker and the heart. Leads for defibrillators are generally similar to pacemaker leads, and are positioned about the heart. Defibrillator leads may be affixed either internally or externally of the heart.
Some leads include one or more coaxial or lateral helical wire coils having a hollow inner passageway that extends the entire length of the wire coil or coils. Other leads may be made with a cable without a hollow inner passageway. The wire coils are surrounded by an electrically insulating material such as a flexible tube, sheath or coating. The insulating material, generally formed of silicone or polyurethane, serves to simultaneously protect the wire coils from body fluids and insulate the wire coils from one another.
While cardiac electrical leads typically have a useful life of many years, over time such leads may become encapsulated by fibrotic tissue against the heart itself or the wall of the vein, or against other surrounding tissue. Encapsulation is especially encountered in areas where the velocity of the flow of blood is low. The fibrotic tissue can be very tough, which makes it difficult to remove the lead from the area of the heart without causing trauma to the area. When small diameter veins through which a pacemaker lead passes become occluded with fibrotic tissue, separation of the lead from the vein can cause severe damage to the vein, including the possible dissection or perforation of the vein. In such cases, separation of the lead from the vein is usually not possible without restricting or containing movement of the lead, i.e., fixing the lead in position with respect to the patient, in particular, with respect to the patient's vein.
To avoid this and other possible complications, some useless pacemaker or other leads are simply left in the patient when the pacemaker or defibrillator is removed or replaced. However, such a practice can incur the risk of an undetected lead thrombosis, which can result in stroke, heart attack, or pulmonary embolism. Such a practice can also impair heart function, as plural leads can restrict the heart valves through which they pass.
There are many other reasons why removal of a useless lead may be desirable. For example, if there are too many leads positioned in a vein, the vein can be obstructed to the extent that fluid flow through the vein is severely compromised. In addition, multiple leads can be incompatible with one another, thereby interfering with the pacing or defibrillating function. An inoperative lead can migrate during introduction of an adjacent second lead, and mechanically induce ventricular arrhythmia. Other potentially life-threatening complications can require the removal of the lead as well. For example, removal of an infected pacemaker lead may be desirable so as to avoid conditions such as septicemia or endocarditis.
Surgical removal of a heart lead in such circumstances often involves open heart surgery. However, open heart surgery is accompanied by significant risk and cost to the patient, as well as a potential for unintended complications. A variety of methods and apparatuses have been devised as alternatives to open heart surgery for heart lead removal. Several of these methods and apparatuses are described in related patents, such as U.S. Pat. No. 5,697,936, titled “Device for Removing an Elongated Structure Implanted in Biological Tissue”; U.S. Pat. No. 5,507,751, titled “Locally Flexible Dilator Sheath”; U.S. Pat. No. 5,632,749, titled “Apparatus for Removing an Elongated Structure Implanted in Biological Tissue”; U.S. Pat. No. 5,207,683, titled “Apparatus for Removing an Elongated Structure Implanted in Biological Tissue”; U.S. Pat. No. 4,943,289, titled “Apparatus for Removing an Elongated Structure Implanted in Biological Tissue”; U.S. Pat. No. 5,011,482, titled “Apparatus for Removing an Elongated Structure Implanted in Biological Tissue”; U.S. Pat. No. 5,013,310, titled “Method and Apparatus for Removing an Implanted Pacemaker Lead”; U.S. Pat. No. 4,988,347, titled “Method and Apparatus for Separating a Coiled Structure from Biological Tissue”; U.S. Pat. No. 5,423,806, titled “Laser Extractor for an Implanted Object”; U.S. Pat. No. 6,419,974, titled “Radio Frequency Dilator Sheath”, and U.S. Pat. Nos. 6,687,548 and 6,712,826, each titled “Apparatus for Removing an Elongated Structure Implanted in Biological Tissue”, among others. Each of the aforementioned patents is incorporated by reference as if fully set forth herein.
Most of the aforementioned patents describe manual, or mechanical, devices that are used for removing an implanted structure, such as a pacemaker lead. Others describe newer non-mechanical techniques, such as laser extraction and radio frequency extraction. These newer techniques have been effective in many cases when the amount and/or placement of fibrous growth that surrounds the implanted lead renders manual extraction difficult or impossible. One example of an effective device that uses radio frequency extraction to enable the physician to cut away the heavy growth is the PERFECTA® electrosurgical dissection sheath, available from Cook Vascular Incorporated, of Leechburg, Pa. The PERFECTA® sheath utilizes an intermittent discrete RF dissecting arc between bipolar electrodes located at the sheath's distal end. This sheath enables the physician to separate, with directed precision, a transvenous lead from its fibrous binding attachments.
Although the prior art devices have been found to be reasonably effective in many situations, physicians continue to encounter particularly difficult situations in which existing extraction devices provide unsatisfactory or inconsistent results. Due to the multiplicity of factors that may contribute to the difficulty in extracting an implanted lead, a technique that may be effective in one instance, may not provide similarly successful results in another instance. For example, manual devices normally are provided with single or telescoping flexible sheaths. Such sheaths, generally formed from a polymer, have the flexibility to enable the sheath to traverse tortuous pathways in the vessel. However, such sheaths may lack sufficient strength to cut through particularly tough tissue growth and calcification around the implanted lead. Laser and radio frequency devices normally utilize metallic sheaths. Such sheaths provide a good deal of strength to enable the sheath to cut through fibrous growths. However, some growths are resistant to metallic sheaths, and these sheaths may also lack the flexibility desired to maneuver tortuous pathways.
It would be desirable to provide a device and tip structure that is effective for removing implanted leads from a vessel, that is easy to operate, and that is versatile enough to overcome many of the obstacles that may be encountered in such operations with existing devices.